The generation of 3-dimensional effects based upon the projection of two different perspective images being viewed in the left and right eyes is known in prior art. Typically two images of the same object are prepared with a small change in the visual perspective of the image. These images are then viewed in such a manner that each eye of the observer only sees one of the images. The visual process then interprets the two separate images as a single 3-dimensional image. This can be achieved in a variety of manners.
Steroscopic viewers require the use of two distinct images which are viewed through two distinct optical paths.
Composite images can be prepared by superimposing the two separate images using two different coloured inks, e.g. red and blue. When viewed through a device containing suitable red and blue filters each eye only sees one of the component images and reconstructs the 3-D image.
The two images can be projected onto a screen using polarised (linear or circular) light. Again, suitable viewing devices enable the viewer to reconstruct the 3-D image. Many devices are described as LCD shutter devices. These use liquid crystalline materials to provide a filter to each eye. The device is electronically controlled so that the shutters are activated sequentially. This allows the viewer to see first one image through the left eye and later the other image through the right eye.
The idea of using cholesteric liquid crystal (CLC) based pigments to generate these effects is described in WO 99/02340. The pigments described have a changing helical pitch which makes them reflective in a wide range of wavelengths. They comprise a bilayer of polymerized CLC material, wherein each layer exhibits a non-linear pitch distribution throughout its thickness direction and as a result shows reflection of a broad wavelength band with asymmetrical reflection characteristics. The pitch gradient is achieved by mixing together a polymerizable CLC material and a non-polymerizable nematic LC material, coating the mixture onto a substrate, annealing to achieve planar alignment and curing e.g. by UV irradiation. Upon curing phase segregation of the non-polymerizable nematic LC material and the polymerized CLC material occurs. This leads to a pitch distribution including regions with high pitch and regions with low pitch within the material. The bilayer is then prepared by laminating together two similar single CLC layers with non-linear pitch distribution and asymmetrical reflection characteristics in such a manner that the resulting bilayer has symmetrical reflection characteristics. The pigments can be prepared in both right and left handed forms which means that they reflect right or left handed circularly polarised light respectively. Also described is a system whereby the composite image is viewed through a filtering device manufactured from similar broad band cholesteric liquid crystal materials.
WO 96/10208 describes the generation of images utilising CLC materials by interlacing two images in an array form on a polarisation encoded medium.
U.S. Pat. No. 5,692,226 discloses a technique for securing motion pictures by generating two images of differing polarisation using CLCs.
U.S. Pat. No. 5,457,554 describes a 3D-image comprising two images of left- and right-handed CLC inks comprising solid CLC platelets or flakes.
U.S. Pat. No. 5,398,131 relates to a stereoscopic image with left- and right-handed-LC inks, which may comprise, e.g., encapsulated CLC materials. Further described are inks comprising crosslinkable CLC silicones that are oriented at high temperatures of 60–90° C. and made into solid films by thermal curing or photocuring.
However, the methods described in prior art have several drawbacks. The CLC pigments and flakes described in WO 99/02340 and U.S. Pat. No. 5,457,554 require a complicated production process. The methods and apparatus described in WO 96/10208 and U.S. Pat. No. 5,692,226 require complicated arrangements of optical components and multiplexing or patterning techniques. The method described in U.S. Pat. No. 5,398,131 requires the CLC inks to be mixed or superimposed to form a stereo pair of images and, where curable materials are involved, requires high processing temperatures.